Ubuntu moved to GNOME Shell from Unity and thrown away the Unity7 and Unity8 shell. It means that users lost a lot of behaviours from the interface of the Unity shell, but in term of graphics, the two shells are pretty the same.
One of the less important behaviours that changed is the position of the ‘Show Applications’ icon in the Dash (emm… pardon, in the Dock I mean!). In Unity, it was at the top of the Dash, in the new Ubuntu GNOME interface it’s at the bottom of the Dock.
The new Ubuntu Dock, which is based on Dash to Dock GNOME Shell extension, allows you to put the Dock on the bottom of the desktop, but not to change the position of the ‘Show Applications’ icon/button.
The workaround is to use the command line and type:
gsettings set org.gnome.shell.extensions.dash-to-dock show-apps-at-top true
To make it persistent, instead you must use these commands as root:
echo show-apps-at-top=true >> /usr/share/glib-2.0/schemas/10_ubuntu-dock.gschema.override glib-compile-schemas /usr/share/glib-2.0/schemas/